ECE21112 Module 6.1: Materials Types and Applications

There are three basic classifications of materials: metals, ceramics, and polymers
Classification is based on chemical make-up and atomic structure
Some materials fall into one distinct group or another, with some intermediates (e.g. composites, biomaterials, semiconductors)

Metallic elements with large numbers of non-localized (free) electrons
Good conductors of electricity and heat, opaque, generally reflective (when polished), strong yet deformable
Extensively used in structural applications

Grouped into two classes: ferrous and nonferrous alloys
- Ferrous alloys: iron-based alloys, include steels and cast irons
- Nonferrous alloys: all alloys that are not iron-based

Produced in larger quantities than any other metal type
3 factors contributing to widespread use:
1. Iron-containing compounds exist in abundant quantities in the earth's crust
2. Metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying, and fabrication techniques
3. Extremely versatile, with a wide range of mechanical and physical properties
Principal disadvantage: susceptibility to corrosion

Iron-carbon alloys that may contain appreciable concentrations of other alloying elements
Mechanical properties sensitive to carbon content (normally less than 1 wt%)
Classified according to carbon concentration (low, medium, and high)

Contain only residual concentrations of impurities other than carbon and a little manganese
Generally contain less than about 0.25 wt% C and are unresponsive to heat treatments intended to form martensite; strengthening is accomplished by cold work
Relatively soft and weak but have outstanding ductility and toughness

Produced in the greatest quantities
Contain less than about 0.25 wt% C and are unresponsive to heat treatments intended to form martensite; strengthening is accomplished by cold work
Generally soft and weak but have outstanding ductility and toughness
Applications: automobile body components, structural shapes (I-beams, channel and angle iron), sheets used in pipelines, buildings, bridges, and tin cans

Have carbon concentrations between about 0.25 and 0.60 wt%
Applications: railway wheels and tracks, gears, crankshafts, other machine parts and high-strength structural components
Plain medium-carbon steels: have low hardenabilities and can be successfully heat treated only in very thin sections and with very rapid quenching rates

Normally have carbon contents between 0.60 and 1.4 wt%
Hardest, strongest, and least ductile of the carbon steels
Almost always used in a hardened and tempered condition
Applications: cutting tools and dies for forming and shaping materials, knives, razors, hacksaw blades, springs, and high-strength wire

Highly resistant to corrosion (rusting) in a variety of environments, especially the ambient atmosphere
Predominant alloying element is chromium; a concentration of at least 11 wt% Cr is required
Corrosion resistance may also be enhanced by nickel and molybdenum additions

With carbon contents above 2.14 wt%
The most common cast iron types are gray, nodular, white, malleable, and compacted graphite
Gray Iron: the carbon and silicon contents of gray cast irons vary between 2.5 and 4.0 wt% and 1.0 and 3.0 wt%, respectively
Ductile (or Nodular) Iron: has mechanical characteristics approaching those of steel
White Iron: extremely hard but also very brittle
Malleable Iron: has relatively high strength and appreciable ductility or malleability
Compacted Graphite Iron (CGI): higher thermal conductivity, better resistance to thermal shock, and lower oxidation at elevated temperatures

Copper and Its Alloys: mechanical and corrosion-resistance properties of copper may be improved by alloying
Aluminum and Its Alloys: characterized by a relatively low density, high electrical and thermal conductivities, and resistance to corrosion in some common environments
Magnesium and Its Alloys: extremely light, with a density of 1.7 g/cm3
Titanium and Its Alloys: extremely strong, with room temperature tensile strengths as high as 1400 MPa (200,000 psi)
Refractory Metals: extremely high melting temperatures
Superalloys: have superlative combinations of properties
Noble Metals: expensive (precious) and superior or notable (noble) in properties